Method for fabricating a through-hole interconnection substrate

ABSTRACT

A blind hole ( 3 ) is formed on a substrate ( 1 ) from a first side of the substrate toward a second side of the substrate ( 1 ). A conductor ( 11 ) is filled in the blind hole ( 3 ). The substrate ( 1 ) is removed from the opposite side to expose the conductor ( 13 ) filled in the blind hole ( 3 ).

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Division of Application No. 10/701,635, now U.S.Pat. No. 7,217,890, filed Nov. 6, 2003, which claims the benefit ofJapanese Patent Application P 2002-324135, filed Nov. 7, 2002 in theJapanese Patent Office, the disclosure of which is incorporated hereinin its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for fabricating a through-holeinterconnection substrate and a through-hole interconnection substrate.More specifically, the present invention is adapted for a high-densitythree-dimensional packaging of stacking a silicon IC chip and the likeor to a contact thereof. The present invention is also adapted for asilicon optical bench for implementing an optical device such as a laserdiode, a photodiode and an optical waveguide.

According to the present invention, a metal for a conductor is filled inmicro-holes for through-hole electrodes. The through hole electrodes areutilized for interconnecting wiring patterns formed on front and backsurfaces of a silicon substrate, to be employed as electrodes orcontacts, and to form bumps.

2. Description of the Related Art

An example of a related art technology for filling metal in micro-holesis a molten-metal suction method disclosed in Japanese Patent Laid-OpenNo. 2002-158191. According to this method, a molten metal is filled inthe holes by means of a pressure difference. An example of a method forforming bumps on one surface of a substrate simultaneously with thisfilling work, is one in which metal layers are formed in the peripheriesof openings of the micro-holes, followed by the metal filling by themolten-metal suction method.

In the molten-metal suction method, heat sometimes deteriorates adhesionof a heat-resistant sheet, thus making it impossible to fill the metalfully in the ends of the micro-holes.

Specifically, when the melting temperature of the metal material in useexceeds 350° C. (degrees centigrade) during the filling work, such hightemperature is beyond a tolerance of the heat-resistant sheet.

SUMMARY OF THE INVENTION

In order to solve the above problems, a first aspect of the invention isdirected to a method for fabricating a through-hole interconnectionsubstrate. The method includes forming a blind hole in a substrate froma first side of the substrate toward a second side of the substrate,forming a conductor in the blind hole, and removing a portion of thesubstrate from the second side of the substrate to expose an end of theconductor.

The conductor may be molten and pressurized into the blind hole.

The method may include the step of forming an insulated layer on asurface of the substrate and an inner wall of the blind hole.

The substrate may be etched from the opposite side.

A second aspect of the invention is directed to a through-holeinterconnection substrate. The through-hole interconnection substrateincludes a substrate having a through-hole and a conductor protrudingthrough the through-hole. The substrate is formed with a blind holeextending from a first side of the substrate toward a second side of thesubstrate, the conductor is formed in the blind hole by pressurizingmolten conductor material, and a portion of the substrate and an endportion of the conductor are removed from the second side of thesubstrate, exposing the conductor filled in the blind hole.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects and advantages of the invention will becomemore apparent by describing in detail exemplary embodiments thereof withreference to the attached drawings in which:

FIG. 1 is an exploded perspective view of a three-dimensional multilayerdevice.

FIGS. 2A to 2E are cross-sectional views of an exemplary embodiment ofan insulator substrate according to the invention, showing steps offorming through-hole interconnections.

FIGS. 3A to 3D are cross-sectional views of an exemplary embodiment of asemiconductor substrate according to the invention, showing steps offorming through-hole interconnections.

FIGS. 4A to 4E are cross-sectional views of the semiconductor substrate,showing steps following FIG. 3D.

FIGS. 5A to 5C are schematic views showing steps of a molten-metalsuction method.

FIG. 6A is a schematic view of an apparatus for use in photo assistedelectro-chemical etching.

FIG. 6B is a schematic view showing a principle of the photo assistedelectro-chemical etching.

DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS

Exemplary embodiments of the invention will now be described withreference to the accompanying drawings. The described exemplaryembodiments are intended to assist the understanding of the invention,and are not intended to limit the scope of the invention in any way.

Referring to FIG. 1, a multilayer device 100 includes IC (IntegratedCircuit) chips 101, 102, and 103 as three stacked layers. Multilayerdevice 100 includes a sensor chip 104 on IC chip 103. IC chips 101, 102,and 103 include through-hole interconnections 101 a, 102 a, and 103 a inperipheral edges thereof, respectively. Through-hole interconnections101 a, 102 a and 103 a electrically connect IC chips 101, 102 and 103with each other. Sensor chip 104 includes gas sensor 104 a, pressuresensor 104 b, and IR sensor 104 c on a surface thereof.

A method for fabricating multilayer device 100 includes the steps ofprocessing a work, forming a circuit pattern, and bonding a wire. Thework is processed as below.

Fabrication of a work or a through-hole interconnection substrate of aninsulated material will be described with reference to FIGS. 2A to 2E(the case where the work is a substrate is assumed in the descriptionbelow).

The work is fabricated by the steps of forming blind holes (refer toFIG. 2A), forming metal layers (refer to FIG. 2B), and filling moltenmetal (FIGS. 2C and 2D).

Referring to FIG. 2A, a plurality of micro-holes 3 are formed on onesurface 5 of a glass substrate 1. Micro-holes 3 are made blind.Thickness T of glass substrate 1 is larger than depth D of eachmicro-hole 3 from one surface 5.

For example, a DRIE (Deep Reactive Ion Etching) method, a laser method,a micro drill method or a sandblast method may be applied to formmicro-holes 3. The DRIE is an ICP-RIE (Inductively CoupledPlasma-Reactive Ion Etching) method. The laser method employs a laserfor drilling. The micro drill method employs a micro drill (microdiameter drill) for drilling. In the sandblast method, micropowder issprayed.

Additionally, the substrate is not limited to glass substrate 1. Forexample, a ceramic, a resin or a composite material thereof is alsoapplicable as long as it has heat resistance higher than a meltingtemperature of a metal to be filled therein. The thickness of thesubstrate is on the order of several ten micrometers (μm) to severalcentimeters (cm). The diameter and depth of each micro-hole are on theorder of several nanometers (nm) to several millimeters (mm). There areno limitations in the number of micro-holes to be formed on thesubstrate.

Referring to FIG. 2B, metal layers 7 are formed in the peripheries ofopenings of the plurality of micro-holes 3, for example, by sputtering,and are patterned into a predetermined shape. The shape of metal layers7 is predetermined to assist in the formation of a bump shape (describedbelow). An example of the metal layer (underlayer) is a layer of Cr andthen Au sputtered with thicknesses of 30 nm and 500 nm, respectively.After coating photoresist thereon, the resist is patterned byphotolithography. The Au and then the Cr are etched by use of thepatterned resist as a mask.

Referring to FIGS. 2C and 5A, a molten-metal bath 67 and substrate 1 aredisposed in a chamber 51. Substrate 1 is supported by substrate holder55. A molten metal 11 is stored in bath 67. Molten metal 11 is agold-tin eutectic solder (Au—20 wt % Sn). Molten metal 11 is heated up,for example, to 330° C. to be molten by a heater 65. The atmosphericpressure in chamber 51 is reduced to vacuum. Next, referring to FIG. 5B,substrate 1 is immersed in molten metal 63 in bath 67. At this stage,molten metal 63 is not filled in micro-holes 3. Next, referring to FIG.5C, after substrate 1 reaches a temperature substantially equal to thatof molten metal 63, chamber 51 is pressurized, for example, to theatmospheric pressure or higher. This pressurization fills molten metal63 into micro-holes 3. Subsequently, substrate 1 is raised from bath 67.At this time, bumps are formed on micro-holes 3.

Glass substrate 1 formed by the above process corresponds to FIG. 2D.Molten metal 11 has been filled and is solidified inside the pluralityof micro-holes 3 of substrate 1, forming blind contacts 13. Theformation of metal layers 7 also forms bumps 15.

Referring to FIG. 2E, the opposite surface (bottom surface) 17 of glasssubstrate 1 is then ground and polished off for flattening. The grindingand polishing allow the bottom surfaces of the filled metal to appear.Thus, contacts 13 are exposed from glass material Ma. Specifically,glass substrate 1 including through-hole interconnections 13 and bumps15 is completed.

Next, the steps of forming micro-holes in a substrate made of a materialother than the insulated material will be described.

Referring to FIG. 3A, a plurality of micro-holes 23 are formed on onesurface 25 of a silicon substrate 21. In this case, micro-holes 23 aremade blind. A thickness T2 of silicon substrate 21 is larger than adepth D2 of each micro-hole 23 from one surface 25.

To the formation of holes 23, for example, the Photo AssistedElectro-Chemical Etching (hereinafter, referred to as a PAECE method) isapplied. In the PAECE, an aqueous hydrofluoric acid (HF) solution isbrought into contact with the front surface of an n-type siliconsubstrate, and lights of a xenon lamp are irradiated onto the backsurface thereof. The silicon substrate functions as an anode. A platinumplate in the aqueous hydrofluoric acid solution functions as a cathode.A voltage is applied between the silicon substrate and the platinumplate.

Specifically, referring to FIG. 6A, an apparatus 70 includeselectrolytic bath 71 storing electrolyte 72 of the HF solution.Apparatus 70 includes a cathode electrode 73 immersed in theelectrolyte, and silicon substrate 21. Apparatus 70 includes a DC power74 between silicon substrate 21 and cathode electrode 73. Apparatus 70includes a light source 75 placed outside an electrolytic bath 71.Apparatus 70 includes an infrared filter 76 between electrolytic bath 71and light source 75.

On surface 21 b of the silicon substrate, a V-groove 21 a is formed byuse of KOH in advance. Lights are radiated from light source 75, passthrough filter 76, and are irradiated onto back surface 21 c of thesilicon substrate, which coincides with V-groove 21 a. During thisirradiation, current flows between substrate 21 and electrode 73.

Referring to FIG. 6B, V-groove 21 a is selectively etched to form ahole. Specifically, by the irradiation of lights 75 a onto back surface21 a of the silicon substrate, carriers (positive holes) are produced onback surface 21 c. These carriers concentrate on the tip end of thebottom of V-groove 21 a, and the tip end is intensively etched.

The substrate is not limited to silicon substrate 21. The substrate maybe made of, for example, a chemical compound, a semiconductor or ametal, as long as it has heat resistance greater than the meltingtemperature of the metal to be filled therein. The thickness of thesubstrate is the order of several ten micrometers to severalcentimeters. The diameter and depth of each micro-hole are the orders ofseveral nanometers to several millimeters. There are no limitations inthe number of micro-holes to be formed on the substrate.

A DRIE method, a laser method, a micro drill method or a sandblastmethod may be applied to a substrate of a non-insulated material inplace of the PAECE method.

Referring to FIG. 3B, an insulated layer 27 is formed on the inner wallsof micro-holes 23 and the surface of the substrate. For example, a SiO2film, a SiN film or the like is formed by use of a method such asthermal oxidization, CVD or coating of a spin-on-glass film. Thethickness of insulated layer 27 is the order of several ten nanometersto several millimeters.

Next, referring to FIG. 3C, metal layers 29 are formed by sputtering inthe peripheries of openings of micro-holes 23, and patterned into apredetermined shape. The shape of metal layers 29 is predetermined toassist in the formation of a bump shape (described below). An example ofthe metal layer (underlayer) is a layer of Cr and then Au sputtered withthicknesses of 30 nm and 500 nm, respectively. After coating photoresistthereon, the resist is patterned by photolithography. The Au and thenthe Cr are etched by use of the patterned resist as a mask.

Referring to FIG. 3D, a molten metal 33 is filled in micro-holes 23 ofsilicon substrate 21 by the molten-metal suction method. Subsequently,substrate 21 is raised from the molten metal bath 67. At this time,bumps 37 (refer to FIG. 4A) are formed on micro-holes 23.

Silicon substrate 21 after the process will be described with referenceto FIG. 4A. Molten metal 33 has been filled in the plurality ofmicro-holes 23, and formed the plurality of contacts 35. Bumps 37 areformed on metal layers 29. As described above, the surface of siliconsubstrate 21 is covered with insulated layer 27.

Referring to FIG. 4B, the opposite surface (bottom surface) 39 ofsilicon substrate 21 is ground and polished. The grinding and polishingare stopped back from insulated layer 27 formed in micro-holes 23.Thickness T3 of silicon substrate 21 is larger than depth D3 of eachmicro-hole 23 on which insulated layer 27 is provided and in whichmolten metal 33 is filled.

Referring to FIG. 4C, only the substrate material is etched, forexample, by chemical etching. This etching allows the bottom portions ofthe micro-holes (that is, contacts 35 as filled metal covered with theinsulated layer) to appear in the order of several micrometers. Platethickness T4 of silicon substrate 21 is made smaller than length D4 ofeach contact 35. The bottom portions of the micro-holes may be exposedfrom the start only by, for example, the chemical etching, withoutgrinding and polishing, other than in the method described above.

Referring to FIG. 4D, an insulated layer 41 is formed on the surface ofthe exposed substrate material. A process temperature during theformation of the insulated layer 41 is set at a temperature lower than amelting point of the filled metal. This set temperature prevents thefilled metal from melting and falling out of micro-holes 23 during theoperation. There are no limitations on the material of insulated layer41, except that it must be possible to form insulated layer 41 at aprocess temperature lower than the melting point. The thickness ofinsulated layer 41 is the order of several micrometers to several tenmicrometers.

Specifically, if the filled metal is gold-tin eutectic solder (Au—20 wt% Sn) with the melting point of 280° C., a SiO₂ film with a thickness of5 μm is deposited at 200° C. by plasma CVD. Again, the opposite surface(bottom surface) 39 of the substrate is ground and polished, exposingthe bottoms of the metal-filled portions. Thus, the through-holeinterconnections are completed.

Silicon substrate 21 after the process will be described with referenceto FIG. 4E. The surfaces of material Mb of silicon substrate 21 iscovered with insulated layer 27 and insulated layer 41. Contacts 35 withbumps 37 made of metal layers 29 are formed. The surface of thesubstrate material is covered with the insulated layer, and there is nopotential risk that the filled metal would contaminate the substratematerial.

Thus, according to an aspect of the invention, a substrate is formedwith a blind hole. Next, the inner wall of the hole and the surface ofthe substrate are formed with an insulated material, except in the caseof a substrate formed of an insulated material. A metal layer is formedaround an opening of the hole. A molten-metal suction method is employedto fill a metal in the hole and to form a bump.

Thus, according to the method, the sealing of the hole on one side bythe substrate itself requires no heat-resistant sheet, and allowssealing not to be broken by heat.

In a case of a substrate of an insulated material, after filling ametal, the bottom surface is ground and polished to expose a filledmetal. This completes a through-hole interconnection.

Next, in a case of a substrate without an insulated material, afterfilling a metal, the bottom surface is ground and polished in the samemanner. However, the grinding and polishing are stopped back from theinsulated layer formed in a micro-hole. Thereafter, only a substratematerial is etched, using, for example, chemical etching, exposing thebottom of the micro-hole. The insulated layer at the bottom of themicro-hole is employed as a protection layer against etching. The reasonnot to grind and polish the filled metal in the micro-hole is to preventthe attaching or dispersing of a metal powder to or in the substratematerial and the resulting contamination of the substrate. In a case ofa substrate of a single crystal, for example, chemical etching aftergrinding and polishing can remove a fractured layer on the polishedsurface that is produced by grinding and polishing. This effectivelyremoves defects such as micro-cracks on the surface of the substrate.

Next, an insulated layer is formed on the exposed surface of thesubstrate. A process temperature during the formation of the insulatedlayer is set at a temperature less than melting point of the filledmetal. This prevents the filled metal from melting and flowing outduring the operation. Thereafter, again, the bottom of the substrate isground and polished to expose a metal filled portion. This completes athrough-hole interconnection. The surface of the substrate is coveredwith an insulated layer, and no contamination due to the filled metaloccurs.

Although the invention has been described above by reference to certainembodiments of the invention, the invention is not limited to theembodiments described above. Modifications and variations of theembodiments described above will occur to those skilled in the art, inlight of the above teachings. The scope of the invention is defined withreference to the following claims.

1. A method for fabricating a through-hole interconnection substrate,comprising: forming a blind hole in an insulating or semiconductingsubstrate from a first side of the insulating or semiconductingsubstrate toward a second side of the insulating or semiconductingsubstrate; forming a conductor in the blind hole; and removing a portionof the insulating or semiconducting substrate from the second side ofthe insulating or semiconducting substrate to expose an end of theconductor, wherein the step of forming the conductor in the blind holecomprises introducing a molten conductor material into the blind hole,and wherein the step of introducing the molten conductor material intothe blind hole is implemented by applying a pressure greater thanatmospheric against the substrate and molten conductor material.
 2. Themethod of claim 1, wherein the molten conductor material is a metal. 3.The method of claim 1, wherein the blind hole is completely filled bythe conductor.
 4. The method of claim 1, wherein a metal layer is formedaround the periphery of the blind hole.
 5. The method of claim 4,wherein the metal layer is arranged along an inner wall of the blindhole and on the first side of the substrate adjacent to the perimeter ofthe blind hole.
 6. The method of claim 1, wherein the blind hole isformed to a depth less than the thickness of the substrate.
 7. Themethod of claim 6, wherein, after the step of removing a portion of thesubstrate, the resultant thickness of the substrate is less than theoriginal depth of the blind hole.
 8. The method of claim 1, furthercomprising forming a bump on the first side of the substrate, whereinthe bump is electrically connected to the conductor formed in the blindhole.
 9. The method of claim 1, further comprising forming a pluralityof blind holes.
 10. The method of claim 1, wherein the step of formingthe conductor in a blind hole comprises: arranging the insulating orsemiconducting substrate and a molten metal bath within an enclosedchamber; reducing the pressure in the chamber to a vacuum; immersing theinsulating or semiconducting substrate in the molten metal bath; andincreasing the pressure in the chamber to level approximately equal tobut not less than atmospheric pressure.
 11. The method of claim 10,wherein the melting temperature of the substrate is higher than themelting temperature of the conductor.
 12. The method of claim 1, whereinthe step of removing a portion of substrate comprises cutting andpolishing.
 13. The method of claim 1, further comprising: forming afirst insulated layer on the first surface of the substrate and an innerwall of the blind hole.
 14. The method of claim 13, further comprising:etching the substrate from the second side so that a portion of theconductor covered by the first insulated layer protrudes from an etchedsecond surface.
 15. The method of claim 14, further comprising: forminga second insulating layer on the etched second surface, wherein thesecond insulating layer covers the portion of the conductor thatprotrudes from the etched second surface.
 16. The method of claim 15,wherein the processing temperature of the formation of the secondinsulating layer is lower than the melting point of the conductor. 17.The method of claim 15, further comprising: removing a portion of thesecond insulating layer so that the conductor is exposed.
 18. The methodof claim 17, wherein the step of removing a portion of the secondinsulating layer comprises cutting and polishing.
 19. The method ofclaim 1, wherein the substrate consists essentially of material selectedfrom the group consisting of glass, ceramic, resin, a compositeincluding glass, ceramic or resin, and a semiconductor.